This invention relates to heteroporphyrin nanostructures and composites thereof with incorporated metals. It is known that certain porphyrins in aqueous solution can form J-aggregates (off-set stacked molecules with aligned transition dipoles). The coherent coupling of the transition dipoles of porphyrin monomers gives rise to aggregate absorption bands that are significantly red-shifted relative to the monomer bands. Additional optical properties of the aggregates include giant resonance light scattering, which imparts intense color to a colloidal solution of such materials when viewed at an angle to the direction of propagation, and possible nonlinear optical properties.
These aggregates are typically in the form of fractal objects or nanoscale flecks of the aggregated porphyrin. An example of such fractal structures is reported in N. Micali et al., “Fractal Structures in Homo- and Heteroaggregated Water Soluble Porphyrins,” J. Phys. Chem. B 104, 9416-9420 (2000).
The lack of linearity in the structure of these aggregates is a disadvantage for many possible applications of such materials where a well-defined morphology, such as nanotubes or nanorods, is desirable. This invention comprises a method for making nanotubular heteroporphyrin J-aggregates possessing a novel linear configuration and the nanotubes made thereby. The nanotubes comprise at least two types of porphyrin moieties with at least one positively charged porphyrin moiety and at least one negatively charged porphyrin moiety. It further comprises the nanostructures resulting from the metallization of these porphyrin nanotubes and the method of making them.
The formation of nanorods, fibers, tubules, helical ribbons, and sheets using a single porphyrin type as the molecular subunit has been previously reported, for example, by Furhop et al., “Micellar Rods and Vesicular Tubules Made of 14′″, 16′″-Diaminoporphyrins,” J. Am. Chem. Soc. 115 (1993) p. 11036-11037, Siggel et al., “Photophysical and Photochemical Properties of Porphyrin Aggregates,” Ber. Bunsenges. Phys. Chem. 100 (1996) p. 2070-2075; Schwab et al., “Porphyrin Nanorods,” J. Phys. Chem B 107 (2003) p. 11339-11345; and Rotomskis et al., “Hierarchical Structure of TPPS4 J-Aggregates on Substrate Revealed by Atomic Force Microscopy,” J. Phys. Chem. B 108 (2004) p. 2833-2383.